The present invention relates to a process and system for measuring without contact the distance of a moving body from a fixed part.
The present invention has been developed with particular attention paid to the field of numeric-control machine tools, but it may be applied to any field where it is required to measure, with a high degree of precision and without contact, the position of a moving body in an area space having dimensions ranging between a few centimeters and tens of meters.
A system widely used on cartesian-type machines employs optical straightedges set along the three axes of movement of the moving body. Each optical straightedge measures the position of the moving body along the corresponding axis, and, in order to determine the position of the body in space, it is assumed that the three axes are set at 90xc2x0 with respect to one another. This assumption inevitably introduces errors in the case where the axes of movement of the machine are not perfectly at right angles to one another.
To prevent this type of error, attempts have been made to develop systems for measuring the position of a moving body that are independent of the drive system that imparts motion on the moving body. The said systems may be identified as measuring systems xe2x80x9cwithout contactxe2x80x9d in so far as they do not require a mechanical contact between the fixed part and the object to be measured. The systems currently known and available on the market can be divided into three categories:
systems using magnetic sensors;
systems based on the measurement of the time of flight of ultrasonic signals, radio signals (radar), or laser beams;
systems based on the angle of reflection of a laser beam; and
laser-interferometry systems.
The systems using magnetic sensors have limited possibilities of application in so far as they need to be very close to (i.e., almost in contact with) the moving body.
Ultrasonic measuring systems based upon the calculation of the time of flight offer poor precision (in the region of 2-3 mm) and are far from easily applicable in the case of distances exceeding 3 meters.
Existing electromagnetic-carrier systems (laser or radio systems) based upon the time of flight afford very poor resolution.
Laser-interferometry systems are not readily applicable to bodies moving in a three-dimensional space in so far as they constantly require a substantial alignment between a laser-beam source and the moving body. These measuring systems moreover present problems when the environment where the measurement is performed has non-homogeneous characteristics, due, for example, to the presence of fumes, smoke, lubricants, and swarf dust or machining residue, as normally occurs in the field of machine tools.
The object of the present invention is to provide a process and a system for measuring the position of a moving body that are not affected by the drawbacks referred to above.
In accordance with the present invention, the above object is achieved by a process and a system having the characteristics that form the subject of the ensuing claims.
The present invention is essentially based upon the application of the principle of interferometry to radio waves and ultrasonic waves for the implementation of direct measuring systems that can be used even in opaque environments and in non-linear three-dimensional space.